1. Field of the Invention
The present invention relates to a diaphragm valve; and more particularly relates to a diaphragm valve having a weir.
2. Brief Description of Related Art
FIGS. 1a to 1d show different parts of a known weir-type diaphragm valve. In FIG. 1a, a diaphragm valve is sealed by a membrane, the diaphragm (1), which must repeatedly travel from a sealed position, against the body weir (2) to an open position. The diaphragm (1) is typically opened with a metal stud (3) embedded within the membrane. An outer seal of the diaphragm (1) is fully constrained while the center of the diaphragm (1) typically experiences the majority of travel to facilitate the open and closed positions. The shape cycles between convex and concave extremes for closed and open positions respectively. As a result, locations of greatest deformation, from bending magnitude and geometry such as thickness, result in the highest material stress. Although the membrane material is chosen to be compliant to these mechanical cycles, it has limitations, especially when combined with certain process requirements, such as extreme cold, heat and/or steam conditions. These conditions weaken the material such that areas of high mechanical stress can limit the life expectancy of the diaphragm. In FIG. 1a, the weir-type diaphragm valve has a backing cushion (4) that acts as a compliant spring membrane between a metal compressor (5) and the plastic diaphragm (1), typically made from Teflon.